Vaginal examination: the only option before labour?

A vaginal examination is a physical examination of a woman's pelvic organs. 

It is frequently performed before delivery to determine the position, tone, length and dilation of the cervix, to assess the bony pelvis as well as the foetal presentation, which can be important in determining whether the baby is poorly positioned, particularly in the presence of risk factors [1]. 

The WHO and the high authority for health do not routinely recommend this practice.
 

A vaginal examination is offered when the woman appears to be in labour. However, in the case of premature rupture of membranes (waters breaking), it is not recommended to perform it routinely if there are no painful contractions [2]. 

During the latent phase, i.e. the first stage of labour, a vaginal examination may be performed every two to four hours, then every hour during the second stage of labour. 
 

Labour can also be artificially induced by vaginal examination. The membrane sweep results from this examination, which can generate sufficient contractions to trigger labour. However, it is a painful procedure that may cause bleeding [3].

What is the purple line?
 

In 1990, scientists first described the appearance of a red/purple discolouration line (though tending to be less visible on darker skin tones) running from the anal margin and extending between the buttocks to reach the top of the buttocks (at the level where the coccyx begins to curve inward) at the onset of the second stage of labour [4]. Their study already suggested at the time that there was a correlation between the length of this line, cervical dilation and the position of the foetal head. 

How does it appear? 

The cause of this line's appearance is still unknown, but several hypotheses have been put forward. Its appearance may be due to vasocongestion (i.e. swelling of body tissues following an increase in vascular blood flow) at the base of the sacrum [8]. This congestion may occur as a result of intra-pelvic pressure as the foetal head descends, which could explain the correlation between the position of the foetal head and the length of the purple line. 

The Michaelis rhombus is a kite-shaped area in the lower back that includes the lower lumbar vertebrae and the sacrum. It is thought that this bony area may shift backwards during advanced labour, pushing the iliac wings apart and increasing the diameter of the pelvis. These normal changes in pelvic shape may offer a potential explanation for the appearance of this line [9].

It has been suggested that the sounds made by women in labour may provide information about the nature of the pain experienced and thus about the stage of labour reached [10]. 

However, assessing labour in this way requires the midwife to know the expectant mother extremely well before birth, which is not always possible. Further research in this area is needed to pave the way for this new non-invasive alternative method.

Although vaginal examination is the standard method for determining cervical dilation and assessing how the foetus is presenting, there may be another alternative for some women! 

One alternative would involve observing a purple line appearing from the base of the buttocks and progressing upwards as labour advances. This line appears on average in 76% of women, making it a worthwhile alternative that deserves to be more widely known.

Another alternative currently under study would be to determine the progress of dilation through maternal vocalisations and pain intensity.